This invention relates to fuel cell systems and, in particular, to manifold assemblies for use with the fuel cell stacks of such systems.
In present day fuel cell systems, manifolds are used to supply and extract fuel and oxidant gasses to and from the fuel cell stack of the system. In some cases, the stack is situated in an enclosure and the enclosure serves as a manifold for one of the gasses. In such an arrangement, a minimum of three additional manifolds is required to provide inlet and exit passages for the other gases of the system. In other cases, where an enclosure does not serve as a manifold, a minimum of four manifolds is required In systems of this type, it is also customary to compress the manifolds against the stack. An example of a stack compression system is described for example in copending U.S. patent application Ser. No. 09/651,921, filed Aug. 31, 2000, assigned to the same assignee hereof. In systems of this type it is also conventional to provide a manifold seal assembly for the external manifolds of the system. A typical seal assembly is disclosed, for example, in U.S. Pat No. 4,467,018.
FIG. 1 shows a typical fuel cell stack 1 in which four manifolds are employed. As shown, the stack 1 includes a number of fuel cell assemblies 11A and electrolyte matrices 11B which are stacked on one another. The arrangement of these components is such that the reactant gases flow in the stack 1 in cross-flow configuration. More particularly, the fuel and oxidant gases flow into respective anode and cathode inlet manifolds 2A and 3A, respectively, and then through the stacked cell assemblies. Exhausted fuel and oxidant gases are then extracted from the cell assemblies via anode and cathode outlet manifolds 2B and 3B. Manifold seal assemblies 4 are also provided and act as seals between the manifolds 2A, 3A, 2B and 3B and the stack 1.
More particularly, as shown in FIG. 2, each of the fuel cell assemblies 11 is comprised of a cathode electrode 12, cathode corrugated current collector 13, bipolar plate 14, anode corrugated current collector 15, and anode electrode 16. The bipolar plates 14 include end flaps 14A at each end which provide flat sealing surfaces as discussed in U.S. Pat. Nos. 5,773,161, 5,399,438 and 4,514,475.
These flat surfaces together result in flat vertical peripheral areas 1A for the stack 1, while the end plates 6 provide flat horizontal peripheral areas 1B for the stack. It is against these flat peripheral areas that the anode and cathode manifolds 2A, 2B, 3A and 3B are sealed. Each manifold seal assembly 4 includes a stack side compressible gasket 4A, a dielectric frame assembly 4B and a manifold side compressible gasket 4C, all of which interface with a respective one of the manifolds. These components permit each seal assembly not only topside sealing but also to limit the electrolyte movement from the top to the bottom of the stack, to limit the electrolyte movement from the stack across the dielectric frame assembly to the manifold, and to allow differential movement between the stack and manifold.
More particularly, each gasket 4A provides a seal between the bipolar plates 14 of the fuel cell assemblies 11 and the dielectric frame assembly 4B. The gaskets 4A are further adapted to limit undesirable transport of electrolyte from the positive to negative lend of the stack. If unchecked this electrolyte migration causes the cells at the negative end of the stack to flood and depletes cells of electrolyte from the positive end. Methods of adapting the gaskets 4A in this way are disclosed, for example, in U.S. Pat. Nos. 4,591,538, 4,643,954, 4,761,348 and 5,110,692. These methods, while they reduce electrolyte migration, do not eliminate all the transport and also add cost to the fuel cell stack 1.
The dielectric frame assemblies 4B provide electrical isolation between the stack 1 and the associated metallic manifolds. As shown in FIG. 1, a typical frame assembly includes horizontal and vertical members 5A, 5B which are joined at joints 5C via aligned slots 5D, 5E and a key 5F. This configuration allows for the differential movement between the stack and the frame assembly (see, e.g., U.S. Pat. No. 4,414,294). To withstand stresses caused by the differential movement, the frame assemblies 4B require high-density ceramics. These ceramics must also be highly polished for assuring required voltage isolation, as described in U.S. patent application No. 09/736,549, filed on Dec. 13, 2000, also assigned to the same assignee hereof. As can be appreciated, the need for high-density, highly polished ceramics also increases the overall cost of the fuel cell stack 1.
While the frame assembly of FIG. 1 includes opposing horizontal and opposing vertical members, the term xe2x80x9cframe assemblyxe2x80x9d as used herein is intended to mean an assembly that includes at least two opposing frame members and, hence, includes within its meaning assemblies that have opposing horizontal members only, and assemblies that have both opposing horizontal members and opposing vertical members. As also used herein the term xe2x80x9csupporting frame assemblyxe2x80x9d is intended to mean a frame assembly that supports one or more members of another frame assembly, and the term. xe2x80x9csupported frame assemblyxe2x80x9d is intended to mean a frame assembly having one or more of its members supported by another frame assembly.
It is therefore an object of the present invention to provide a manifold and manifold sealing assembly which overcomes the above-discussed disadvantages of prior assemblies.
It is also an object of the present invention to provide a manifold and manifold sealing assembly having a reduced number of parts.
It is a further object of the present invention to provide a manifold and manifold sealing assembly which permit a reduction in the number of parts of the dielectric frame assemblies and in the number of gaskets.
It is also an object of the present invention to provide a manifold and manifold sealing assembly which permit the use of simplified bipolar plates.
In accordance with the principles of the present invention, the above and other objectives are realized in a manifold and manifold sealing assembly including a plurality of frame assemblies and a plurality of manifolds. One or more of the frame assemblies is a supporting frame assembly and one or more of the frame assemblies is a supported frame assembly. Each supporting frame provides structural support for a part of one of the supported frame assemblies facing a face of the fuel cell stack adjacent to the face faced by the supporting frame assembly. In further accordance with the invention, the manifold abutting a supporting frame assembly is adapted to sealing engage with areas of the manifold abutting the associated supported frame assembly.
In the embodiment of the invention to be disclosed hereinafter, each supporting frame assembly includes a vertical member adjacent to a vertical side of the associated fuel cell stack face which supports at its upper and lower ends upper and lower horizontal members of the associated supported frame assembly. These horizontal members are, in turn, situated adjacent to upper and lower ends of the associated fuel cell stack face.
Also, in this embodiment, each manifold situated adjacent to a supporting frame assembly has a peripheral flange having a vertical side with an extension which extends beyond the vertical end of the associated fuel cell stack face. This extension serves as a sealing member for a vertical side of the peripheral flange of the manifold situated adjacent to the supported frame. The latter manifold has a central region which extends beyond the vertical edge of the associated fuel cell stack face so as to permit the sealing engagement.
Additionally, in the disclosed embodiment, a supported frame assembly abutting a given face of the fuel cell stack is supported by two supporting frame assemblies abutting the faces of the stack which are adjacent the opposite vertical sides of the given face. In the disclosed four face stack, two supporting frame assemblies abut opposite faces of the stack and support two supported frame assemblies which abut the other two opposite faces of the stack. In this case, each supporting frame assembly includes vertical members adjacent opposite vertical edges of the associated fuel cell stack face, one of which supports upper and lower horizontal members of the supported frame assembly abutting one of the adjacent fuel cell stack faces and the other of which supports upper and lower horizontal members of the supported frame assembly abutting the other of the adjacent fuel cell stack faces.